The haemoglobin polymorphism in Atlantic cod (Gadus morhua L.); genotypic differences in somatic growth and in maturing age in natural populations. In: The propagation of cod Gadus morhua L.: an international symposium, Arendal, 14 - 17 June 1983
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The two common alleles at the polymorphic haemoglobin locus HbI (Sick, 1961) in the Atlantic cod (Gadus morhua L.) code for proteins whose functional properties are differentially influenced by environmental temperatures (Karpov and Novikov, 1980). In the present study HbI genotypic mean lengths in a total of 275 immature specimens (0.5 - 1.5 year of age) from 8 samples taken in the Trondheimsfjord and Oslofjord during 1977-1981 were investigated by rank correlation analysis. In males the overall genotypic mean length rank was HbI^2-2 >HbI^1-2 >HbI^1-1, while i n females HbI^l-2 >HbI^2-2 >HbI^1-1; both ranks were highly significant. The age at first spawning (A_m) was determined by otolith reading in a sample of 118 male cod caught during spawning in the Trondheimsfjord in 1983. In this sample the individual A_m ranged from 4-7 years with a significantly lower mean for the HbI^2-2 genotype. The A_m of heterozygotes was intermediate but not significantly lower than for the HbI^1-1 genotype. Some population genetic and aquacultural implications of these results are briefly discussed.